The present invention relates to a novel solid state ceramic composite electrolyte.
Ceramics generally possess a number of desirable properties, including markedly high resistance to abrasion, heat and corrosion compared to metallic materials. Certain ceramics, such as stabilized bismuth solid oxides, stabilized ceria solid oxides and zirconia solid oxides are ionically conductive materials suitable for use as solid electrolytes. However, due to extreme brittleness, their application has been limited despite their other excellent properties.
A number of attempts have been made to increase toughness of ceramic materials by compounding them with another material including ceramic or metal whiskers such as silicon carbide whiskers. Composites with ceramic matrices and ductile metal inclusions such as those produced by Lanxide Corporation show high fracture toughness when compared to ordinary ceramic materials. See for example U.S. Pat. Nos. 4,824,622; 4,847,220; 4,822,759; 4,820,461; and related U.S. Pat. No. 4,871,008. These composites are a chaotic, generally discontinuous, random metal dispersion in a ceramic composite body. They are prepared by a slow controlled oxidation of molten aluminum to alumina oxide, leaving behind approximately 5% of the parent metal. See also C. A. Anderson et al., Ceram. Eng. Sci. Proc., 9 [7-8] pp. 621-626 (1988); and M. S. Newkirk et al., Ceram. Eng. Sci. Proc., 8 [7-8] pp 879-885 (1987).
P. Ducheyne et al., J. Materials Science 17(1982) 595-606 discloses a bioglass composite produced by immersing premade porous fiber skeletons into molten bioglass to prepare metal fiber reinforced bioglass. These porous fiber skeletons produce random, chaotic, disordered support matrices and the process is applicable only to bioglasses.
U.S. Pat. No. 4,764,488 discloses a high toughness ceramic composite of the fiber-reinforced type wherein metal fibers having the shape of triangular waves forming bent portions alternating on the opposite sides with an angle Õ of the bent portions in a range between 60xc2x0 and 165xc2x0 and a d/H ration of between 0.025 and 0.6. While the discrete, discontinous fibers, unidirectionally anchored fiber reinforcement employed in the 488 patent improve the toughness of the ceramic, this technique does not solve the problem of crack propagation and ultimate failure.
U.S. Pat. No. 4,776,866 discloses a whisker-reinforced ceramic matrix composite comprising a principal crystal phase selected from the group consisting of anorthite, barium-stuffed cordierite and mixed cordierite/anthorite prepared by extrusion of ceramic batches comprising an extrusion vehicle and a solid component comprising essentially inorganic whiskers and powdered glass.
The novel composite employed in the practice of this invention is mechanically tough. When subjected to intentionally severe mechanical stress, such as bending a sheet in half and restraightening it, the crack that resulted was limited to the stress or fold line.
The present invention provides a ductile solid electrolyte composite comprising a continuous, ordered, repeating ductile metallic array surrounded by and supporting an ionically conductive ceramic matrix. The preferred form of the solid electrolyte is a planar structure which can be fabricated into various configurations such as tubes, arcuate sections, corrugated structures or flat plates.